Presentation on theme: "Www.tececo.com 1 New Materials Based on the Addition of Reactive Magnesia to Hydraulic Cements. All I ask is that the industry think about what I am saying."— Presentation transcript:
www.tececo.com 1 New Materials Based on the Addition of Reactive Magnesia to Hydraulic Cements. All I ask is that the industry think about what I am saying. John Harrison B.Sc. B.Ec. FCPA. Hobart, Tasmania, Australia
www.tececo.com 2 Materials - the Key to Sustainability The choice of materials controls emissions, lifetime and embodied energies, maintenance of utility, recyclability and the properties of wastes returned to the biosphere.
www.tececo.com 3 The Construction Industry The built environment is our footprint on earth. TecEco estimate that building materials comprise some 70% of materials flows. Calcined minerals and their derivatives are the main materials used to construct the built environment. –Globally around 2 billion tonnes of calcined minerals (cement, lime and magnesia) are produced annually. –Portland cement is made by calcining limestone with clay and concrete made with it is the most widely used material on Earth. –Global Portland cement production is in the order of 1.7 billion tonnes. The largest producers of Portland cement are China at over 500 million tonnes followed by India at over 110 million tonnes. Globally this amounts to over 6 cubic kilometres of concrete per year. Downloaded from www.dbce.csiro.au/ind- serv/brochures/embodied/embodied.htm (last accessed 07 March 2000)
www.tececo.com 4 Embodied Energy of Building Materials Downloaded from www.dbce.csiro.au/ind- serv/brochures/embodied/embodied.htm (last accessed 07 March 2000) Concrete has a relatively low embodied energy
www.tececo.com 5 Embodied Energy in Buildings Downloaded from www.dbce.csiro.au/ind- serv/brochures/embodied/embodied.htm (last accessed 07 March 2000) But because so much is used there is a huge opportunity for sustainability
www.tececo.com 6 Sustainability = High Performance Sustainability is not just about reducing emissions. Other properties of concrete such as the amount of cement required for a given strength, durability, embodied energy, insulating capacity, weight etc. are also relevant. Concretes should not be thought of as just cement and aggregate. They will become a composite material with a range of tailored properties offering vastly improved overall performance as well as meeting specific performance criteria such as strength. As an ideal building material concrete should include other properties not usually provided such as insulating capacity and the ability to utilise wastes. –All sorts of other materials such as industrial mineral wastes, sawdust, wood fibres, waste plastics etc. could be added for the properties they impart. –More attention paid to the micro engineering of the material as well as the chemistry would result in improved properties. Concretes can cost affectively be everything we would like them to be!
www.tececo.com 7 Emissions Calcined mineral materials and their derivatives used in construction such as Portland cement, lime and magnesia are made from carbonates. The process of calcination involves driving off chemically bound CO 2 with heat. MCO 3 MO + CO 2 Heating requires energy. 98% of the worlds energy is derived from fossil fuels. Fuel oil, coal and natural gas are mainly directly or indirectly burned to produce the energy required for calcining of metal carbonates releasing CO 2. Most of the embodied energy in the built environment is in concrete. The production of cement for concretes accounts for around 10% of global anthropogenic CO 2.
www.tececo.com 8 Opportunities for Sustainability The CO 2 released by chemical reaction from the calcined materials in TecEco Eco-cement concretes can be captured during manufacture and reabsorbed on a widely distributed basis in eco- cements. A system using TecEco Eco-Cements to construct the built environment therefore offers enormous opportunities for sequestration, particularly if combined with mineral sequestration utilising magnesium silicates in a combined process. Other TecEco cements are also much more sustainable but for different reasons that include durability and the use of less cement to make more material.
www.tececo.com 9 Talked about –Rheology Workability, time for and method of placing and finishing –Shrinkage Cracking, crack control –Durability and Performance Permeability and Density Sulphate and chloride resistance Carbonation Corrosion of steel and other reinforcing Delayed reactions (eg alkali aggregate and delayed ettringite) –Bonding to brick and tiles –Efflorescence Rarely discussed –Sustainability issues Emissions and embodied energies Should the discussion be more about how we could fix the material, overcoming rather than tolerating and mitigating these problems? Issues with OPC Concrete
www.tececo.com 10 Engineering Issues are Mineralogical Issues Problems with Portland cement concretes are usually resolved by the band aid application of engineering fixes. They are rarely discussed in terms of the mineralogy. e.g. –Use of calcium nitrite, silanes, cathodic protection or stainless steel to prevent corrosion. –Use of coatings to prevent carbonation. –Crack control joins to mitigate the affects of shrinkage cracking. –Plasticisers to improve workability, glycols to improve finishing. Many of the problems with Portland cement are better fixed by fundamentally fixing the mineralogy! The flaw in the mineralogy of Portland cement concretes is the presence of Portlandite which is too soluble, mobile and reactive. The TecEco technology is not a band aid, it is a fundamental fix.
www.tececo.com 11 TecEco Technology - Simple Yet Ingenious? The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. -- Sir William Bragg The TecEco technology demonstrates that magnesia, provided it is reactive rather than dead burned (or high density, periclase type), can be beneficially added to cements in excess of the amount of 5 mass% generally considered as the maximum allowable by standards Reactive magnesia is essentially amorphous magnesia produced at low temperatures and finely ground.
www.tececo.com 12 TecEco Concretes – A Blending System TecEco concretes are a system of blending reactive magnesia, Portland cement and usually a pozzolan with other materials.
www.tececo.com 13 Reactivity Overcomes Delayed Hydration Problems. Delayed hydration leads to dimensional distress. –Magnesium was banned in Portland cements because when it goes through the high temperature process of making Portland cement it becomes periclase. It is dead burned, hydrates slowly and causes dimensional distress. –Dead burned lime is much more expansive than dead burned magnesia(1), a problem largely forgotten by cement chemists. TecEco have demonstrated that highly amorphous reactive magnesia can beneficially be added to concrete formulations –The reactivity of magnesia is a function of the state of disorder (lattice energy), specific surface area and glass forming impurities. The state of order or disorder is expressed in lattice energy and is dependent on the temperature of calcining. Specific surface area relates particle size. Make a particle small enough and it will react with just about anything. Glass forming impurities are formed when reactive magnesia reacts at high temperatures with impurities such as iron. A new TecEco kiln technology which combines calcining and grinding should make it possible to calcine at lower temperatures and produce more reactive magnesia with reduced problems due to impurities as well as capture CO 2. –(1) Ramachandran V. S., Concrete Science, Heydon & Son Ltd. 1981, p 358-360.
www.tececo.com 14 Why Replace Portlandite with Brucite? Portlandite (Ca(OH) 2 ) is not a suitable concrete matrix mineral. Ca(OH) 2 is reactive, carbonates readily and being soluble can act as an electrolyte. TecEco remove Portlandite in reactions with Pozzolans. Brucite is much less soluble, mobile or reactive, does not act as an electrolyte or carbonate as readily. The addition of magnesia which hydrates forming brucite improves the rheology, uses up bleed water as it hydrates, filling in the pores, increasing the density, reducing permeability, reducing shrinkage and providing long term pH control with many consequences including greater durability. In porous eco-cements brucite carbonates forming stronger minerals. The consequences of removing Portlandite (lime) with the pozzolanic reaction and filling the voids between hydrating cement grains with brucite, an insoluble alkaline mineral, need to be considered.
www.tececo.com 15 Portlandite Compared to Brucite PropertyPortlandite (Lime)Brucite Density2.232.9 Hardness2.5 – 3 Solubility (cold)1.85 g L -1 in H 2 O at 0 o C0.009 g L -1 in H 2 O at 18 o C. Solubility (hot).77 g L -1 in H 2 O at 100 o C.004 g L -1 H 2 O at 100 o C Solubility (moles, cold)0.000154321 M L -1 0.024969632 M L -1 Solubility (moles, hot)0.000685871 M L -1 0.010392766 M L -1 Solubility Product (K sp )5.5 X 10 -6 1.8 X 10 -11 ReactivityHighLow FormMassive, sometime fibrous Usually fibrous Free Energy of Formation of Carbonate G o f - 64.62 kJ.mol -1 - 19.55 kJ.mol -1
www.tececo.com 16 TecEco Formulations Three main formulation strategies so far: –Tec-cements (e.g. 10% MgO, 90% OPC.) Contain more Portland cement than reactive magnesia. –Reactive magnesia hydrates in the same rate order as Portland cement forming Brucite which uses up water reducing the voids:paste ratio, increasing density and possibly raising the short term pH. Reactions with pozzolans are more affective. After all the Portlandite has been consumed Brucite controls the long term pH which is lower and due to its low solubility, mobility and reactivity results in greater durability. –Other benefits include improvements in density, strength and rheology, reduced permeability and shrinkage and the use of a wider range of aggregates without reaction problems. –Enviro-cements (e.g. 25-75% MgO, 25-75% OPC) In non porous concretes brucite does not carbonate readily. –High proportions of magnesia are most suited to toxic and hazardous waste immobilisation and when durability is required. Strength is not developed quickly. –Eco-cements (egg 50-75% MgO, 50-25% OPC) Contain more reactive magnesia than in tec-cements. Brucite in porous materials carbonates –Forming stronger fibrous mineral carbonates. –Presenting huge opportunities for abatement.
www.tececo.com 18 Porosity and Magnesia Content Note that TecEco eco-cements require a porous environment.
www.tececo.com 19 Basic Chemical Reactions Notice the low solubility of brucite compared to Portlandite and that magnesite is stronger and adopts a more ideal habit than calcite & aragonite
www.tececo.com 20 Greater Strength Tec-cements can be made with at least 25% less binder for the same strength. Possible reasons for –Low binder/total solids ratio –More rapid strength development even with pozzolans Reactive magnesia is an excellent plasticiser and results in: –Denser, less permeable concrete. –A significantly lower voids/paste ratio. Higher early pH initiating more effective silicification reactions –The Ca(OH)2 normally lost in bleed water is used internally for reaction with pozzolans. –Super saturation caused by the removal of water by magnesia as it hydrates. Concrete technologists are obsessed by strength. They should be more interested in durability!
www.tececo.com 21 Rapid Water Reduction Water is required to plasticise concrete for placement, however once placed, the less water over the amount required for hydration the better. Magnesia rapidly removes water as it hydrates. Less water results in less shrinkage and cracking and improved durability. Concentration of alkalis and increased density result in greater strength.
www.tececo.com 22 Concretes have a high percentage of voids. On hydration magnesia expands 116.9 % filling voids and surrounding hydrating cement grains. Brucite is 44.65 mass% water. Lower voids:paste ratios than water:binder ratios result in less bleed water and greater density. Greater density results in greater strength, more durable concrete with a higher salt resistance and less corrosion of steel etc. Self compaction of brucite may add to strength. –Compacted brucite is as strong as CSH (Ramachandran, Concrete Science p 358) Durability & Strength - Increased Density
www.tececo.com 24 Hypothetical Tec-Cement Concrete Strength Development Curve The possibility of high early strength gain with added pozzolans is of great economic importance.
www.tececo.com 25 Durability - A Lower More Stable Long Term pH Eh-pH or Pourbaix Diagram The stability fields of hematite, magnetite and siderite in aqueous solution; total dissolved carbonate = 10 -2 M. In TecEco cements the long term pH is governed by the low solubility and carbonation rate of brucite and is much lower at around 10.5 -11, allowing a wider range of aggregates to be used, reducing problems such as AAR and etching. The pH is still high enough to keep Fe 2 O 3 and Fe 3 O 4 stable in reducing conditions.
www.tececo.com 26 The Passive Coating of Iron Oxide The passive coating on steel is iron oxide. According to the Pourbaix diagram it is magnesite but some authors such as Neville report the oxide is γ Fe3O(1). One of the problems associated with examining iron oxides is that they change rapidly from one form to another and are therefore difficult to characterise(2). The author would be interested in definitive information of any papers on this subject! (1) Neville, A. M. Properties of Concrete, 4th Ed. Pearson Prentice Hall, England, 2003, page 563.
www.tececo.com 27 Durability – Reduced Delayed Reactions A wide range of delayed reactions can occur in Portland cement based concretes –Delayed alkali silica and alkali carbonate reactions –The delayed formation of ettringite and thaumasite –Delayed hydration of minerals such as dead burned lime and magnesia. Delayed reactions cause dimensional distress and possible failure.
www.tececo.com 28 Durability – Reduced Delayed Reactions (2) Delayed reactions do no occur to the same extent in TecEco Cements. –A lower long term pH results in reduced reactivity after the plastic stage. –Potentially reactive ions are trapped in the structure of brucite. –Ordinary Portland cement concretes can take years to dry out however Tec-cement concretes are dried out from the inside by the water demand of reactive magnesia as it hydrates.
www.tececo.com 29 Durability – Carbonation Carbonates are the stable phases of both calcium and magnesium. Carbonates lower the pH of concretes compromising the stability of the passive oxide coating on steel. The Portlandite in Portland cement concretes carbonates readily starting at the surface. Brucite in tec - cement concretes carbonates less readily (for the main kinetic pathway) because: –The carbonation reaction has a less negative Gibbs free energy. G o r Brucite = -19.55 G o r Portlandite = -64.62 –Carbon dioxide cannot enter the dense impermeable concrete matrix. –The magnesium carbonates that form at the surface of tec – cement concretes expand, sealing off further carbonation. Eco-Cement Concretes –Magnesite is formed deliberately and is stronger and more acid resistant than calcite or aragonite.
www.tececo.com 30 Durability – Reduced Permeability As bleed water exits ordinary Portland cement concretes it creates an interconnected pore structure that remains in concrete allowing the entry of aggressive agents such as SO 4 --, Cl - and CO 2 TecEco tec - cement concretes are a closed system. They do not bleed as excess water is consumed by the hydration of magnesia. –As a result TecEco tec - cement concretes dry from within, are denser and less permeable, and cement powder is not lost near the surfaces.
www.tececo.com 31 Reduced Shrinkage Dimensional change such as shrinkage results in cracking and reduced durability
www.tececo.com 32 Reduced Cracking in TecEco Cement Concretes After Richardson, Mark G. Fundamentals of Durable Reinforced Concrete Spon Press, 2002. page 212. Cracking, the symptomatic result of shrinkage, is undesirable for many reasons, but mainly because it allows entry of gases and ions reducing durability. Cracking can be avoided only if the stress induced by the free shrinkage strain, reduced by creep, is at all times less than the tensile strength of the concrete. Reduced in TecEco tec- cements because they do not shrink.
www.tececo.com 33 Corrosion in Portland Cement Concretes Passive Coating Fe 3 O 4 intact Both carbonation, which renders the passive iron oxide coating unstable or chloride attack (various theories) result in the formation of reaction products with a higher electrode potential resulting in anodes with the remaining passivated steel acting as a cathode. Corrosion Anode: Fe Fe ++ + 2e- Cathode: ½ O 2 + H 2 O +2e - 2(OH) - Fe ++ + 2(OH) - Fe(OH) 2 + O 2 Fe 2 O 3 and Fe 2 O 3.H 2 O (iron oxide and hydrated iron oxide or rust) The role of chloride in Corrosion Anode: Fe Fe ++ + 2e- Cathode: ½ O 2 + H 2 O +2e - 2(OH) - Fe ++ +2Cl - FeCl 2 FeCl 2 + H 2 O + OH - Fe(OH) 2 + H + + 2Cl - Fe(OH) 2 + O 2 Fe 2 O 3 and Fe 2 O 3.H 2 O Iron hydroxides react with oxygen to form rust. Note that the chloride is recycled in the reaction and not used up.
www.tececo.com 34 Reduced Steel Corrosion A pH of over 8.9 is maintained for much longer and steel remains passive due to a stable oxide coating. Brucite does not react readily resulting in reduced carbonation rates and reactions with salts. Concrete with brucite is denser and carbonation is expansive, sealing the surface preventing further access by moisture, CO 2 and salts. Brucite is less soluble and traps salts as it forms resulting in less ionic transport to complete a circuit for electrolysis and less corrosion. Free chlorides and sulfates originally in cement and aggregates bound by magnesium –Magnesium oxychlorides or oxysulfates are formed. ( Compatible phases in hydraulic binders that are stable provided the concrete is dense and water kept out.)
www.tececo.com 35 Brucite has always played a protective role during salt attack. Putting it in the matrix of concretes in the first place makes sense. Brucite does not react with salts because of its low solubility (reactivity, mobility) and lower pH (reactivity) –Ksp brucite = 1.8 X 10 -11 –Ksp Portlandite = 5.5 X 10 -6 - 5 orders of magnitude Durability - Reduced Salt Attack
www.tececo.com 36 Improved Workability Finely ground reactive magnesia acts as a plasticiser. –Improving rheology –Lower water cement ratio results in greater strength and reduced porosity. –The proportion and cost of binders and plasticisers can be reduced.
www.tececo.com 37 Reasons for Improved Workability There are also surface charge affects and water reducing agents are not required. Reactive Magnesia is a plasticiser as well.
www.tececo.com 38 Rheology TecEco concretes are –very homogenous –very thixotropic and react well to energy input. (Slump is therefore not a good measure of workability) TecEco concretes with the same water/binder ratio have a lower slump but greater plasticity and workability.
www.tececo.com 39 Dimensionally Neutral TecEco Tec - Cement Concretes During Curing? Portland cement shrinks around.05%. Over the long term much more (>.1%). –Mainly due to chemical shrinkage, plastic and drying shrinkage, as well as carbonation. Hydration: –When magnesia hydrates it expands: MgO (s) + H 2 O (l) Mg(OH) 2 (s) 40.31 + 18.0 58.3 molar mass 11.2 + liquid 24.3 molar volumes –Up to 116.96% solidus expansion depending on whether the water is coming from stoichiometric mix water, bleed water or from outside the system. In practice much less as the water comes from mix and bleed water. –So far we have not observed shrinkage in TecEco tec - cement concretes (10% substitution OPC) also containing fly ash. –The water lost by Portland cement as it shrinks is used by the reactive magnesia as it hydrates eliminating shrinkage.
www.tececo.com 40 Volume Changes on Carbonation Carbonation: –Consider what happens when Portlandite carbonates: Ca(OH) 2 + CO 2 CaCO 3 74.08 + 44.01 100 molar mass 33.22 + gas 28.10 molar volumes 18.22% shrinkage. Cracks appear allowing further carbonation. –Compared to brucite forming magnesite as it carbonates: Mg(OH) 2 + CO 2 MgCO 3 58.31 + 44.01 84.32 molar mass 24.29 + gas 28.10 molar volumes 15.68% expansion and densification of the surface preventing further ingress of CO 2 and carbonation. Self sealing? Combined - Curing and Carbonation are close to Neutral. –At some ratio, thought to be around 10% reactive magnesia and 90% OPC volume changes cancel each other out. –More research is required for both tec - cements and eco-cements to accurately establish volume relationships.  The molar volume (L.mol-1)is equal to the molar mass (g.mol-1) divided by the density (g.L-1).
www.tececo.com 42 Are the Texts all Wrong About Carbonation? Most texts maintain the carbonation reaction is one between ions in solution yet carbonation is observable in very dry conditions. The transport of carbon dioxide is much more rapid in air than in water and adherence to Le Chateliers principal would also indicate dry conditions as the removal or water as a product would help the reaction Ca(OH) 2 + CO 2 CaCO 3 + H 2 O ( Gof - 64.62 kJ.mol-1) To proceed towards products (the right). The highly negative Gibbs free energy of the reaction indicates this should occur spontaneously. The author would be very interested in some definitive information on this as most of the texts seem to take a bet both ways! Please contact me if you know more about this than me!
www.tececo.com 43 Safety – Reduced Fire Damage The main phase in TecEco tec - cement concretes is brucite. The main phases in TecEco eco-cements are magnesite and hydromagnesite. Brucite, magnesite and hydromagnesite are excellent fire retardants and extinguishers. At relatively low temperatures –Brucite releases water and reverts to magnesium oxide. –Magnesite releases CO2 and converts to magnesium oxide. –Hydromagnesite releases CO2 and water and converts to magnesium oxide. Fires are therefore not nearly as aggressive resulting in less damage to structures. Damage to structures results in more human losses that direct fire hazards.
www.tececo.com 44 TecEco Eco-Cements - Solving Waste Problems The best thing to do with wastes is if at all possible to use them. If they cannot directly be used then they have to be immobilised. Concretes represent a cost affective option: Chemically and physically enviro-cements are more suited to toxic and hazardous waste immobilisation than either lime, Portland cement or Portland cement lime mixes and they are more predicable than geopolymers. In a Portland cement brucite matrix –OPC takes up lead, some zinc and germanium –Brucite and hydrotalcite are both excellent hosts for toxic and hazardous wastes. Brucite has a layered structure and traps neutral compounds between the layers. –Heavy metals not taken up in the structure of Portland cement minerals or trapped within the brucite layers end up as hydroxides. The pH which is controlled in the long term by brucite is around 10.52, and is an ideal long term value at which most heavy metal hydroxides are relatively insoluble. TecEco cements are also more durable, dense, impermeable and homogenous. They do not bleed water, are not attacked by salts in ground or sea water and dimensionally more stable with less cracking.
www.tececo.com 45 Toxic and Hazardous Waste Immobilisation The brucite in TecEco cements has a structure comprising electronically neutral layers and is able to accommodate a wide variety of extraneous substances between the layers and cations of similar size substituting for magnesium within the layers and is known to be very suitable for toxic and hazardous waste immobilisation. Brucite is an ideal mineral for trapping toxic and hazardous wastes.
www.tececo.com 46 Lower Solubility of Metal Hydroxides
www.tececo.com 47 High Performance = Sustainability=Lower Cost Comprehensive high performance will include improvements in: –Compressive and tensile strength/binder ratios –Durability, insulating capacity, ability to host wastes –Weight etc. etc. Increased durability will result in lower costs/energies/emissions due to less frequent replacement. Improvements in insulating capacity will mean lower lifetime as well as embodied energies in buildings.
www.tececo.com 48 TecEco Concretes - Lower Construction Costs Lower water binder ratio means less binders (eg OPC) for same strength. Faster strength gain even with added pozzolans. Cheaper binders as less energy required and a higher proportion is water. Elimination of shrinkage reducing associated costs. Elimination of bleed water enables finishing of lower floors whilst upper floors still being poured. A high proportion of brucite compared to Portlandite is water and of magnesite compared to calcite is CO 2. –Every mass unit of TecEco cements therefore produces a greater volume of built environment than Portland and other calcium based cements. Less need therefore be used reducing costs/energy/emissions.
www.tececo.com 49 TecEco Concretes - Lower Construction Costs (2) Homogenous, so no under plastic necessary. Because reactive magnesia is also an excellent plasticiser, other costly additives are not required for this purpose. Easier placement and better finishing. A wider range of aggregates can be utilised without problems reducing transport and other costs/energies/emissions. Greater durability reduces costs over time. Reduced or eliminated carbon taxes. Eco-cements can to a certain extent be recycled. TecEco cements utilise wastes many of which improve properties.
www.tececo.com 50 Characteristics of TecEco Cements (1) Portland Cement Concretes Tec-Cement Concretes Enviro-Cement Concretes Eco-Cements Typical Formulations 100 mass% PC8 mass% OPC, 72 mass % PC, 20 mass% pozzolan 20 mass% OPC, 60 mass % PC, 20 mass% pozzolan 50 mass% OPC, 30 mass % PC, 20 mass% pozzolan SettingMain strength from hydration of calcium silicates. Main strength is from hydration of calcium silicates. Magnesia hydrates forming brucite which has a protective role. Magnesia hydrates forming brucite which protects and hosts wastes. Carbonation is not encouraged. Magnesia hydrates forming brucite then carbonates forming magnesite and hydromagnesite. SuitabilityDiverseDiverse. Ready mix concrete with high durability Toxic and hazardous waste immobilisation Brick, block, pavers, mortars and renders. Mineral Assemblage (in cement) Tricalcium silicate, di calcium silicate, tricalcium aluminate and tetracalcium alumino ferrite. Tricalcium silicate, di calcium silicate, tricalcium aluminate, tetracalcium alumino ferrite, reactive magnesia.
www.tececo.com 51 Characteristics of TecEco Cements (2) Portland Cement Concretes Tec-Cement Concretes Enviro-Cement Concretes Eco-Cements Final mineral Assembla ge (in concrete) Complex but including tricalcium silicate hydrate, di calcium silicate hydrate, ettringite, monosulfoaluminat e, (tetracalcium alumino sulphate), tricalcium alumino ferrite hydrate, calcium hydroxide and calcium carbonate. Complex but including tricalcium silicate hydrate, di calcium silicate hydrate, ettringite, monosulfoaluminate, (tetracalcium alumino sulphate), tricalcium alumino ferrite hydrate, calcium hydroxide, calcium carbonate, magnesium hydroxide and magnesium carbonates. Strength (S19-21) Variable. Mainly dependent on the water binder ratio and cement content. Variable. Mainly dependent on the water binder ratio and cement content. Usually less total binder for the same strength development Variable, usually lower strength because of high proportion of magnesia in mix. Variable.
www.tececo.com 52 Characteristics of TecEco Cements (3) Portland Cement Concretes Tec-Cement Concretes Enviro-Cement Concretes Eco-Cements Rate of Strength Developm ent (S28) Variable. Addition of fly ash can reduce rate of strength development. Variable. Addition of fly ash does not reduce rate of strength development. Slow, due to huge proportion of magnesia Variable, but usually slower as strength develops during carbonation process. pH (S20,21) Controlled by Na + and K + alkalis and Ca(OH) 2 in the short term. In the longer term pH drops near the surface due to carbonation (formation of CaCO 3 ) Controlled by Na + and K + alkalis and Ca(OH) 2 and high in the short term. Lower in the longer term and controlled by Mg(OH) 2 and near the surface MgCO 3 High in the short term and controlled by Ca(OH) 2. Lower in the longer term and controlled by MgCO 3 Rheology (S32-35) Plasticisers are required to make mixes workable. Plasticisers are not necessary. Formulations are generally much more thixotropic. Plasticisers are not necessary. Formulations are generally much more thixotropic and easier to use for block making.
www.tececo.com 53 Characteristics of TecEco Cements (4) Portland Cement Concretes Tec-Cement Concretes Enviro-Cement Concretes Eco-Cements Durability( S22-25) Lack of durability is an issue with Portland cement concretes Protected by brucite, are not attacked by salts, do not carbonate, are denser and less permeable and will last indefinitely. Protected by brucite, are not attacked by salts, do not carbonate, are denser and will last indefinitely. Density (S25) Density is reduced by bleeding and evaporation of water. Do not bleed - water is used up internally resulting in greater density Permeabilit y(S28) Permeable pore structures are introduced by bleeding and evaporation of water. Do not bleed - water is used up internally resulting in greater density and no interconnecting pore structures Shrinkage (S36-39) Shrink around.05 -.15 % With appropriate blending can be made dimensionally neutral as internal consumption of water reduces shrinkage through loss of water and magnesium minerals are expansive.
www.tececo.com 54 Characteristics of TecEco Cements (5) Portland Cement Concretes Tec-Cement Concretes Enviro-Cement Concretes Eco-Cements Insulating Properties Relatively low with high thermal conductivity around 1.44 W/mK Depends on formulation but better insulation as brucite is a better insulator Depends on formulation but better insulation as brucite is a better insulator and usually contains other insulating materials Thermal Mass High. Specific heat is.84 kJ/kgK Depends on formulation but remains high Embodied Energy (of concrete) Low, 20 mpa 2.7 Gj.t-1, 30 mpa 3.9 Gj.t-1 (1) Approx 15-30% lower due to less cement for same strength, lower process energy for making magnesia and high pozzolan content(2). Lower depending on formulation(2). Depends on formulation Even lower due to lower process energy for making magnesia and high pozzolan content(2).
www.tececo.com 55 Characteristics of TecEco Cements (6) Portland Cement Concretes Tec-Cement Concretes Enviro-Cement Concretes Eco-Cements Re- cyclability Concrete can only be crushed and recycled as aggregate. Can be crushed and recycled as aggregate. Can be crushed and fines re-calcined to produce more magnesia or crushed and recycled as aggregate or both. Fire Retardant Ca(OH) 2 and CaCO 3 break down at relatively high temperatures and cannot act as fire retardants Mg(OH) 2 is a fire retardant and releases H 2 O at relatively low temperatures. Mg(OH) 2 and MgCO 3 are both fire retardants and release H 2 O or CO 2 at relatively low temperatures.
www.tececo.com 56 Characteristics of TecEco Cements (7) Portland Cement Concretes Tec-Cement Concretes Enviro-Cement Concretes Eco-Cements SustainabilityA relatively low embodied energy and emissions relative to other building products. High volume results in significant emissions. Less binder for the same strength and a high proportion of supplementary cementitous materials such as fly ash and gbfs. Can be formulated with more sustainable hydraulic cements such as high belite sulphoaluminate cements. A wider range of aggregates can be used. Greater durability. A high proportion of supplementary cementitous materials such as fly ash and gbfs. Can be formulated with more sustainable hydraulic cements such as high belite sulphoaluminate cements. A wider range of aggregates can be used. Greater durability. A high proportion of supplementary cementitous materials such as fly ash and gbfs. Carbonate in porous materials reabsorbing chemically released CO 2 A wider range of aggregates can be used. Greater durability. Carbon emissions With 15 mass% PC in concrete.32 t.t -1 After carbonation approximately.299 t.t -1 With 15 mass% PC in concrete approx.29 t.t -1 After carbonation approximately.26 t.t -1 Could be lower using supplementary cementitous materials and formulated with other low carbon cement blends. With 11.25 mass % magnesia and 3.75 mass % PC in concrete.241 t.t -1 With capture CO 2 and fly ash as low as.113 t.t -1
www.tececo.com 57 TecEco Challenging the World Although the technology is new and not yet fully characterised, TecEco challenge universities governments and construction authorities to come to grips with the new cement technology and quantify performance in comparison to ordinary Portland cement and other competing materials. At TecEco will do our best to assist. Negotiations are underway in many countries to organise supplies to allow such scientific endeavour to proceed. The invention of the new TecEco cement system is an enormous opportunity for the world to take materials science, which is the key to sustainability, more seriously.
www.tececo.com 58 Addressing Issues in Concrete Science Addressing the research objectives of concrete science. –Durability salt resistance and steel corrosion may become problems of the past. Lower use of materials and energy over time saving money and the environment. –Lower more stable long term alkalinity. Reduced AAR and steel corrosion etc. –Better rheology. Lower water cement ratio, less shrinkage, and easier placement. –Other improved properties: Greater density, adjustable placing and finishing times. Fire retarding properties –Lower Costs Making reactive magnesia is a benign process with potential for using waste energy and capture of CO 2. A wider range of aggregates including wastes will be available reducing cartage costs and emissions. Water or CO 2 from the air comprise a high mass % and volume % of the magnesium minerals in TecEco cements. Water and CO 2 are free or attract carbon credits Expensive plasticisers are not required
www.tececo.com 59 TecEcos Immediate Focus Form strategic alliances with major companies. Raise money for Research – Around 1 million dollars worth in the pipeline. Concentrate on defined markets for low technical risk products that require minimal research and development and for which performance based standards apply. –Carbonated products such as bricks, blocks, stabilised earth blocks, pavers, roof tiles pavement and mortars that utilise large quantities of waste and products where sustainability, rheology or fire retardation are an issue. (Mainly eco-cement technology using fly ash). –The immobilisation of wastes including toxic hazardous and other wastes because of the superior performance of the technology and the rapid growth of markets. (Eco-cements and tec - cements). –Products such as oil renders and mortars where excellent rheology and bond strength are required. –Products where extreme durability is required. –Products for which weight is an issue. Continue our awareness campaign regarding TecEco cements, the new TecEco kiln design and the Tech Tendon method of prestressing, partial prestressing and reinforcing.
www.tececo.com 60 TecEco Minding the Future TecEco are aware of the enormous weight of opinion necessary before standards can be changed globally for TecEco tec - cement concretes for general use. –TecEco already have a number of institutions and universities around the world doing research. TecEco have received huge global publicity – not all of which is correct and have therefore publicly released the technology. –TecEco research documents are available from TecEco by request. Soon they will be able to be purchased from the web site. –Other documents by other researchers will be made available in a similar manner as they become available. Technology standing on its own is not inherently good. It still matters whether it is operating from the right value system and whether it is properly available to all people. -- William Jefferson Clinton
www.tececo.com 61 TecEco Technology Summary Simple, smart and sustainable? –TecEco cement technology has resulted in potential solutions to a number of problems with Portland and other cements including durability and corrosion, the alkali aggregate reaction problem and the immobilisation of many problem wastes and will provides a range of more sustainable building materials. The right technology at the right time? –TecEco cement technology addresses important triple bottom line issues solving major global problems with positive economic and social outcomes. Climate Change Pollution Durability Corrosion Strength Delayed Reactions Placement, Finishing Rheology Shrinkage Carbon Taxes
www.tececo.com 62 The Magnesium Thermodynamic Cycle
www.tececo.com 63 Manufacture of Portland Cement
www.tececo.com 64 TecEco Eco - Cements for Sustainable Cities
www.tececo.com 65 Manufacture of TecEco-Cements
www.tececo.com 66 Embodied Energy and Emissions Energy costs money and results in emissions and is the largest cost factor in the production of mineral binders. –Whether more or less energy is required for the manufacture of reactive magnesia compared to Portland cement or lime depends on the stage in the utility adding process it is measured. –Utility is greatest in the finished product which is concrete. The volume of built material is more relevant than the mass and is therefore more validly compared. On this basis the technology is far more sustainable than either the production of lime or Portland cement. –The new TecEco kiln technology will result in around 25% less energy being required and the capture of CO2 during production resulting in lower costs and carbon credits. The manufacture of reactive magnesia is a benign process that can be achieved with waste or intermittently available energy.
www.tececo.com 67 Energy – On a Mass Basis Relative to Raw Material Used to make Cement From Manufactur ing Process Energy Release 100% Efficient (Mj.tonne -1 ) From Manufacturin g Process Energy Release with Inefficiencie s (Mj.tonne -1 ) Relative Product Used in Cement From Manufacturi ng Process Energy Release 100% Efficient (Mj.tonne -1 ) From Manufacturin g Process Energy Release with Inefficiencies (Mj.tonne -1 ) Relative to Mineral Resulting in Cement From Manufacturi ng Process Energy Release 100% Efficient (Mj.tonne -1 ) From Manufacturi ng Process Energy Release with Inefficienci es (Mj.tonne -1 ) CaCO 3 + Clay1545.732828.69 Portlan d Cement18073306.81 Hydrated OPC1264.902314.77 CaCO 3 1786.092679.14Ca(OH) 2 2413.203619.80 MgCO 3 1402.751753.44MgO2934.263667.82Mg(OH) 2 2028.472535.59
www.tececo.com 68 Energy – On a Volume Basis Relative to Raw Material Used to make Cement From Manufacturi ng Process Energy Release 100% Efficient (Mj.metre -3 ) From Manufacturin g Process Energy Release with Inefficiencies (Mj.metre -3 ) Relative Product Used in Cement From Manufactur ing Process Energy Release 100% Efficient (Mj.metre -3 ) From Manufacturin g Process Energy Release with Inefficiencies (Mj.metre -3 ) Relative to Mineral Resulting in Cement From Manufactur ing Process Energy Release 100% Efficient (Mj.metre -3 ) From Manufacturing Process Energy Release with Inefficiencies (Mj.metre -3 ) CaCO 3 + Clay4188.937665.75 Portland Cement5692.0510416.45 Hydrated OPC3389.936203.58 CaCO 3 6286.628429.93Ca(OH) 2 5381.448072.16 MgCO 3 4278.395347.99MgO9389.6311734.04Mg(OH) 2 4838.326085.41
www.tececo.com 69 CO 2 Abatement –TecEco Eco-Cements
www.tececo.com 70 Global Abatement Without CO2 Capture during manufacture (billion tonnes) With CO2 Capture during manufacture (billion tonnes) Total Portland Cement Produced Globally 1.80 Global mass of Concrete (assuming a proportion of 15 mass% cement) 12.00 Global CO 2 Emissions from Portland Cement 3.60 Mass of Eco-Cement assuming an 80% Substitution in global concrete use 9.60 Resulting Abatement of Portland Cement CO 2 Emissions 2.88 CO 2 Emissions released by Eco-Cement 2.591.34 Resulting Abatement of CO 2 emissions by Substituting Eco-Cement 0.291.53
www.tececo.com 71 Abatement from Substitution Figures are in millions of Tonnes Building Material to be substituted Realisti c % Subst- itution by TecEco technol ogy Size of World Market (millio n tonnes Substit uted Mass (million tonnes) CO2 Fact ors (1) Emission From Material Before Substituti on Emission/Sequestrati on from Substituted Eco-Cement (Tonne for Tonne Substitution Assumed) Net Abatement Emission s - No Capture Emission s - CO2 Capture Abatem ent - No Capture Abatem ent CO2 Capture Bricks85%250212.50.2859.522.214.171.1249.8 Steel25%8402102.38499.856.629.4443.2470.4 Aluminium20%20.54.118.073.81.10.672.773.2 TOTAL426.620.7633.1114.959.7518.2573.4 Concretes already have low lifetime energies. If embodied energies are improved could substitution mean greater market share?
www.tececo.com 72 Tripling Mineral Sequestration As a method of capturing CO 2 the kinetics of the following reactions are being examined: ½Mg 2 SiO 4 + CO 2 MgCO 3 + ½SiO 2 + 95kJ/mole 1 / 3 Mg 3 Si 2 O 5 (OH) 4 + CO 2 MgCO 3 + 2 / 3 SiO 2 + 2 / 3 H 2 O + 64kJ/mole Of the above the second reaction with chrysotile or serpentine as it is sometimes called is favoured as the mineral is abundant. At low partial pressures of CO 2 and relatively low temperatures, MgCO 3 will break down yielding MgO and CO 2. MgCO 3 MgO + CO 2
www.tececo.com 73 Tripling Mineral Sequestration (2) Utilising a closed system such as with TecEco Kiln technology the CO 2 re-emitted can be captured for industrial use (replacing alternative production) or direct sequestration. If the MgO is then used to make eco- cement products the total CO 2 captured is three moles to the mole of serpentinite mined. MgO +H 2 O Mg(OH) 2 Mg(OH) 2 +CO 2 MgCO 3 + H 2 O
www.tececo.com 74 Tripling Mineral Sequestration (3) One tonne of chrysotile will sequester.588 tonnes CO 2 producing 1.263 tonnes of magnesite. 1.263 tonnes of magnesite will yield.538 tonnes of reactive magnesia..588 tonnes CO 2 driven off by the low temperature calcination of magnesia can be captured. The magnesia when it carbonates (directly or via the hydroxide) will yield 1.263 tonnes of magnesite again absorbing a further.588 tonnes of CO 2 A total of 1.176 tonnes of CO 2 can therefore be directly sequestered and a further.588 tonnes captured. Captured CO 2 can be used to replace commercially produced CO 2 or sequestered by other means. Total sequestration possible is therefore three times that possible with direct mineral sequestration alone!